1. Field of the Invention
The invention relates to controlled release compositions and more particularly relates to methods of preparing controlled release compositions such as encapsulated volatile organic liquids.
2. Brief Description of the Invention
The literature is replete with descriptions of prior art methods and techniques for the preparation of devices and compositions which allow for the controlled release of volatile organic liquids. One technique comprises impregnating absorbent particulate solids such as active charcoal, diatomaceous earth, clay, aluminum silicates, silica and like materials with the organic liquid. Over a period of time, the organic liquid vaporizes and is released from the absorbent carrier.
The prior art technique of employing absorbent solid particle carriers as described above has not been entirely satisfactory. Only limited quantities of the volatile organic liquids can be absorbed by the particulate solid carriers (on the order of 10 percent or less, by weight). Also, above the limited levels of absorbability, the particulate solids become wet and difficult to handle, because they lose the fluidity or flowability associated with granular particles and powders.
By the method of the present invention, particles of amorphous silica are employed to encapsulate volatile organic liquids. The resulting capsule compositions will allow the controlled, slow release of vapors over a period of time. The capsule materials are easy to handle and flow with the fluidity associated with granular or powdery solids.